---
title: "Unit 4: Seasons (Optional 3E)"
subtitle: "How does the annual cycle of Earth around the Sun create seasonal temperature variations?"
author: "Earth & Space Science"
format:
html:
toc: true
toc-depth: 3
number-sections: true
theme: cosmo
code-fold: true
self-contained: true
execute:
echo: true
warning: false
---
```{=html}
<style>
@import url('https://fonts.googleapis.com/css2?family=Space+Grotesk:wght@700&family=Inter:wght@400;600;800&display=swap');
.engage-box {
background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
color: white;
padding: 25px;
margin: 20px 0;
border-radius: 15px;
box-shadow: 0 10px 30px rgba(102, 126, 234, 0.3);
}
.explore-box {
background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
color: white;
padding: 25px;
margin: 20px 0;
border-radius: 15px;
box-shadow: 0 10px 30px rgba(240, 147, 251, 0.3);
}
.explain-box {
background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
color: #1a1a1a;
padding: 25px;
margin: 20px 0;
border-radius: 15px;
box-shadow: 0 10px 30px rgba(79, 172, 254, 0.3);
}
.check-understanding {
background: linear-gradient(to right, #667eea, #764ba2);
color: white;
padding: 20px;
margin: 20px 0;
border-radius: 12px;
border-left: 6px solid #fff;
animation: pulse 2s infinite;
}
@keyframes pulse {
0%, 100% { box-shadow: 0 0 20px rgba(102, 126, 234, 0.5); }
50% { box-shadow: 0 0 30px rgba(102, 126, 234, 0.8); }
}
.quiz-section {
background: linear-gradient(135deg, #a8edea 0%, #fed6e3 100%);
padding: 25px;
margin: 25px 0;
border-radius: 15px;
border: 4px dashed #ff6b6b;
}
h1 {
font-family: 'Space Grotesk', sans-serif !important;
font-weight: 800 !important;
font-size: 2.8em !important;
margin-top: 40px !important;
}
h2 {
font-family: 'Space Grotesk', sans-serif !important;
font-weight: 700 !important;
color: #667eea !important;
}
.big-question {
font-family: 'Space Grotesk', sans-serif;
font-size: 2.5em;
font-weight: 800;
background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
-webkit-background-clip: text;
-webkit-text-fill-color: transparent;
margin: 30px 0 20px 0;
text-align: center;
animation: slideIn 0.8s ease-out;
}
@keyframes slideIn {
from { opacity: 0; transform: translateY(-20px); }
to { opacity: 1; transform: translateY(0); }
}
</style>
```
# Engage: Why Do We Have Seasons?
::: {.engage-box}
### 🤔 Initial Question
Many people believe seasons are caused by Earth being closer to or farther from the Sun. Is this correct?
**Fact:** Earth is actually closest to the Sun (perihelion) in early January during Northern Hemisphere winter!
:::
## Interactive: Earth's Orbit Distance
```{ojs}
//| echo: false
Plot = require("@observablehq/plot")
orbitData = [
{month: "Jan", distance: 147.1, season: "Winter (NH)"},
{month: "Feb", distance: 147.8, season: "Winter"},
{month: "Mar", distance: 148.9, season: "Spring"},
{month: "Apr", distance: 150.0, season: "Spring"},
{month: "May", distance: 151.0, season: "Spring"},
{month: "Jun", distance: 151.8, season: "Summer"},
{month: "Jul", distance: 152.1, season: "Summer (NH)"},
{month: "Aug", distance: 151.5, season: "Summer"},
{month: "Sep", distance: 150.5, season: "Fall"},
{month: "Oct", distance: 149.3, season: "Fall"},
{month: "Nov", distance: 148.1, season: "Fall"},
{month: "Dec", distance: 147.3, season: "Winter"}
]
Plot.plot({
title: "Earth-Sun Distance Throughout the Year",
subtitle: "Distance in millions of kilometers",
width: 650,
height: 350,
x: {label: "Month", domain: orbitData.map(d => d.month)},
y: {label: "Distance (million km)", domain: [146, 153]},
marks: [
Plot.line(orbitData, {x: "month", y: "distance", stroke: "#e67e22", strokeWidth: 3}),
Plot.dot(orbitData, {x: "month", y: "distance", fill: "#e67e22", r: 6}),
Plot.text([{month: "Jan", distance: 147.1}], {x: "month", y: "distance", text: d => "Closest!", dy: -15, fill: "red", fontWeight: "bold"}),
Plot.text([{month: "Jul", distance: 152.1}], {x: "month", y: "distance", text: d => "Farthest!", dy: -15, fill: "blue", fontWeight: "bold"})
]
})
```
# Explore: Axial Tilt and Sunlight
## PhET Simulation: Seasons
Explore how Earth's axial tilt creates seasons:
```{=html}
<div style="text-align: center; margin: 20px 0;">
<p><strong>Note:</strong> If the simulation doesn't load, <a href="https://phet.colorado.edu/sims/html/seasons/latest/seasons_en.html" target="_blank">click here to open it in a new tab</a>.</p>
<iframe src="https://phet.colorado.edu/sims/html/seasons/latest/seasons_en.html"
width="800" height="600" allowfullscreen style="border: 2px solid #ccc; border-radius: 10px;"></iframe>
</div>
```
::: {.explore-box}
### 🔬 Exploration Tasks
1. Observe how the angle of sunlight changes throughout the year at different latitudes
2. Compare day length at 45°N during summer vs. winter solstice
3. Notice how the Sun's rays are more direct in summer and more spread out in winter
:::
## Interactive: Sunlight Angle Simulator
```{ojs}
//| echo: false
viewof sunAngle = Inputs.range([0, 90], {
step: 5,
value: 45,
label: "Sun Angle (degrees from horizon):"
})
```
```{ojs}
//| echo: false
// Calculate how sunlight spreads based on angle
spreadFactor = 1 / Math.sin(sunAngle * Math.PI / 180)
intensityPercent = (Math.sin(sunAngle * Math.PI / 180) * 100).toFixed(1)
html`<div style="display: flex; gap: 30px; align-items: center; margin: 20px 0;">
<div style="flex: 1;">
<svg width="300" height="200">
<!-- Ground -->
<rect x="0" y="150" width="300" height="50" fill="#8B4513"/>
<!-- Sun rays -->
<line x1="50" y1="${150 - 100 * Math.tan(sunAngle * Math.PI / 180)}" x2="50" y2="150" stroke="yellow" stroke-width="3"/>
<line x1="100" y1="${150 - 100 * Math.tan(sunAngle * Math.PI / 180)}" x2="100" y2="150" stroke="yellow" stroke-width="3"/>
<line x1="150" y1="${150 - 100 * Math.tan(sunAngle * Math.PI / 180)}" x2="150" y2="150" stroke="yellow" stroke-width="3"/>
<!-- Angle arc -->
<path d="M 50 150 L 50 100 A 50 50 0 0 1 ${50 + 50 * Math.cos((90-sunAngle) * Math.PI / 180)} ${150 - 50 * Math.sin((90-sunAngle) * Math.PI / 180)}" fill="none" stroke="red" stroke-width="2"/>
<text x="70" y="130" fill="red" font-size="14">${sunAngle}°</text>
</svg>
</div>
<div style="flex: 1; padding: 20px; background: #f5f5f5; border-radius: 10px;">
<h4>Energy Intensity</h4>
<p><strong>Relative intensity:</strong> ${intensityPercent}%</p>
<p><strong>Energy spread factor:</strong> ${spreadFactor.toFixed(2)}x</p>
<div style="background: linear-gradient(to right, #ffeb3b ${intensityPercent}%, #ccc ${intensityPercent}%); height: 30px; border-radius: 5px;"></div>
<p style="font-size: 12px; margin-top: 10px;">Higher sun angles = more concentrated energy = warmer temperatures</p>
</div>
</div>`
```
# Explain: The Science of Seasons
::: {.explain-box}
### 🌍 Key Concepts
**Seasons are caused by Earth's 23.5° axial tilt, NOT distance from the Sun.**
1. **Summer:** Your hemisphere is tilted TOWARD the Sun
- Sun appears higher in the sky
- Sunlight hits more directly (concentrated energy)
- Longer days = more heating time
2. **Winter:** Your hemisphere is tilted AWAY from the Sun
- Sun appears lower in the sky
- Sunlight hits at an angle (spread out energy)
- Shorter days = less heating time
:::
## Connection to Climate Change
Understanding seasons helps us understand climate change because:
- **Milankovitch Cycles** involve changes to Earth's tilt over thousands of years
- These orbital changes have driven glacial-interglacial cycles
- We'll explore this in detail in the next lesson!
::: {.check-understanding}
### ✅ Check Your Understanding
1. Why is it WARMER in summer even though Earth is FARTHER from the Sun?
2. How does the angle of sunlight affect heating?
3. Why do the Northern and Southern hemispheres have opposite seasons?
:::
---
::: {.quiz-section}
## 📝 Seasons Quiz
**Question 1:** Earth is closest to the Sun during which month?
- A) July
- B) January
- C) March
- D) September
**Question 2:** What primarily causes Earth's seasons?
- A) Distance from the Sun
- B) Earth's axial tilt of 23.5°
- C) Changes in the Sun's output
- D) Ocean currents
**Question 3:** During Northern Hemisphere summer, the North Pole is:
- A) Tilted away from the Sun
- B) Tilted toward the Sun
- C) Not tilted at all
- D) Experiencing 24 hours of darkness
*Answers: 1-B, 2-B, 3-B*
:::